I don't know if you've ever tried pkzipping a file several times,
pkware says you can zip a file up to 7 times I think.
Anyway, the file doesn't hardly get any smaller at all,
anotherwords, there's no point in doing it.
It's possable some combination might make a smaller file, but
the PC would probably run slower, especially an older PC.
If you want smaller files just use a higher compression setting.